Dc-dc converter and organic light emitting display device using the same

ABSTRACT

There are provided a DC-DC converter and an organic light emitting display device using the same. A DC-DC converter includes a switching module that converts an input voltage into a first voltage through switching operations of a plurality of switches that are turned on or off in response to a pulse width modulation (PWM) signal, and outputs the first voltage; a sensing unit that senses driving current supplied to a load to which the first voltage is provided; and a control module that controls the switching module by generating the PWM signal. The control module is configured to adaptively control the turn-on resistance of the switching module according to the sensed result of the sensing unit. Accordingly, it is possible to provide a DC-DC converter and an organic light emitting display device using the same which has optimal efficiency by adaptively operating according to a load condition.

RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0121374, filed on Oct. 30, 2012, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. Furthermore, the present application is related to a co-pending U.S. application Ser. No. (to be assigned), entitled DC-DC CONVERTER AND ORGANIC LIGHT EMITTING DISPLAY DEVICE USING THE SAME, based upon Korean Application No. 10-2012-0121414, filed on Oct. 30, 2012, in the Korean Intellectual Property Office (KIPO).

BACKGROUND

1. Field

An aspect of the present invention relates to a DC-DC converter and an organic light emitting display device using the same, and more particularly, to a DC-DC converter and an organic light emitting display device using the same which has optimal efficiency by adaptively operating according to a load condition.

2. Description of the Related Art

Among flat panel display devices, an organic light emitting display device displays images using organic light emitting diodes (OLEDs) that emit light through recombination of electrons and holes. The OLED includes an anode electrode, a cathode electrode and a light emitting layer positioned between the anode and cathode electrodes. If current flows through the OLED in the direction from the anode electrode to the cathode electrode, the OLED emits light, thereby expressing a color. In the organic light emitting display device, emission luminance is determined according to the amount of current flowing through the OLED of each pixel. Therefore, a high-luminance image requires more driving current than a low-luminance image. That is, the driving current required to drive pixels of the organic light emitting display device is changed depending on a displayed image. Accordingly, in order to reduce power consumption, a DC-DC converter for driving the pixels of the organic light emitting display device should be designed to have high efficiency throughout the entire range of the driving current.

SUMMARY

Embodiments provide a DC-DC converter and an organic light emitting display device using the same which has optimal efficiency by adaptively operating according to a load condition.

According to an aspect of the present invention, there is provided a DC-DC converter, including: a switching module that converts an input voltage into a first voltage through switching operations of a plurality of switches that are turned on or off in response to a pulse width modulation (PWM) signal, and outputs the first voltage; a sensing unit that senses driving current supplied to a load to which the first voltage is provided; and a control module that controls the switching module by generating the PWM signal, wherein the control module is configured to adaptively control the turn-on resistance of the switching module according to the sensed result of the sensing unit.

According to an aspect of the present invention, there is provided an organic light emitting display device, including: a display panel that has a plurality of pixels and displays a gray scale according to the luminance of an organic light emitting diode in each pixel; a timing controller that provides data in the display panel; and a DC-DC converter that generates first and second voltages for supplying current to the organic light emitting diode by receiving an input voltage, and provides the first and second voltages to the display panel, wherein the DC-DC converter includes: a first converter that converts the input voltage into the first voltage, and outputs the first voltage; a second converter that converts the input voltage into the second voltage, and outputs the second voltage; and a sensing unit that senses driving current supplied to the display panel. The first converter includes: a first switching module that converts the input voltage into the first voltage through switching operations of a plurality of switches that are turned on or off in response to a first PWM signal, and outputs the first voltage to the display panel; and a first control module that controls the switching module by generating the first PWM signal. The second converter includes: a second switching module that converts the input voltage into the second voltage through switching operations of a plurality of switches turned on/off in response to a second PWM signal, and outputs the second voltage to the display panel; and a second control module that controls the second switching module by generating the second PWM signal. The first control module is configured to adaptively control the turn-on resistance of the first switching module, based on the sensed result of the sensing unit, and the second control module is configured to adaptively control the turn-on resistance of the second switching module, based on the sensed result of the sensing unit.

As described above, according to the present invention, it is possible to provide a DC-DC converter and an organic light emitting display device using the same which has optimal efficiency by adaptively operating according to a load condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.

FIG. 1 is a diagram illustrating a DC-DC converter according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an embodiment of the DC-DC converter shown in FIG. 1.

FIG. 3 is a diagram illustrating an embodiment of a switching module shown in FIG. 2.

FIG. 4 is a diagram illustrating an embodiment in which first and second switching units of the DC-DC converter shown in FIG. 2 each has three transistor switches.

FIG. 5 is a diagram illustrating another embodiment of the DC-DC converter shown in FIG. 1.

FIG. 6 is a diagram illustrating an embodiment of a switching module shown in FIG. 5.

FIG. 7 is a diagram illustrating an embodiment in which first and second switching units of the DC-DC converter shown in FIG. 5 each has three transistor switches.

FIG. 8 is a diagram illustrating an organic light emitting display device according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating an embodiment of a DC-DC converter shown in FIG. 8.

FIG. 10 is a diagram illustrating an organic light emitting display device according to another embodiment of the present invention.

FIG. 11 is a diagram illustrating an embodiment of a DC-DC converter shown in FIG. 10.

DETAILED DESCRIPTION

Hereinafter, certain exemplary embodiments according to the present invention will be described with reference to the accompanying drawings. Here, when a first element is described as being coupled to a second element, the first element may be not only directly coupled to the second element but may also be indirectly coupled to the second element via a third element. Further, some of the elements that are not essential to the complete understanding of the invention are omitted for clarity. Also, like reference numerals refer to like elements throughout.

Hereinafter, a direct current to direct current (DC-DC) converter and an organic light emitting display device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram illustrating a DC-DC converter 100 according to an embodiment of the present invention.

Referring to FIG. 1, the DC-DC converter 100 includes a switching module 120, a sensing unit 140 and a control module 160.

The switching module 120 has a plurality of switches, and each of the plurality of switches converts an input voltage VIN applied from the outside of the switching module 120 into a first voltage V1 and outputs the first voltage V1 while being switched in response to a corresponding pulse width modulation (PWM) signal.

The sensing unit 140 senses driving current supplied to a load that receives the first voltage V1 provided from the switching module 120. For example, in a case where the capacity of the load is changed while the first voltage V1 is supplied to the load, i.e., in a case where the driving current supplied to the load is changed, the sensing unit 140 senses, in real time, a change in driving current and informs the control module 160 of the sensed change in driving current.

The control module 160 controls the switching module 120 by generating a PWM signal. The control module 160 is configured to adaptively control the turn-on resistance of the switching module 120 according to the sensed result of the sensing unit 140. In other words, the control module 160 is configured to adaptively control the size of a switch or transistor in the switching module 120 according to a load condition.

The DC-DC converter 100 is a kind of switching regulator. Therefore, switching loss according to the parasitic capacitance of the switch increases when the capacity of the load is small, and driving current increases when the capacity of the load is large. Accordingly, conduction loss according to the turn-on resistance of the switch increases. The control module 160 controls the switching module 120 so that the switching loss is minimized when the capacity of the load is small, and the conduction loss is minimized when the capacity of the load is large. As a result, the DC-DC converter 100 according to this embodiment can have optimal efficiency, regardless of various load conditions. For reference, the parasitic capacitance of the switch is in proportion to the size of the switch, i.e., the length (L) and width (W) of the transistor. Thus, as the size of the transistor is smaller, the parasitic capacitance is smaller. Accordingly, in a case where several switches with a small size are used, loss according to the parasitic capacitance can be reduced. The DC-DC converter 100 may generate the first voltage V1 by increasing or decreasing the input voltage VIN, and may generate the first voltage V1 by reversing the polarity of the input voltage VIN. The amplitude of the driving current supplied to the load coupled to an output terminal of the DC-DC converter 100 may be variable. For example, the first voltage V1 may be a voltage ELVDD applied to an anode of an organic light emitting diode of each pixel in an organic light emitting display device or a voltage ELVSS applied to a cathode of the organic light emitting diode of each pixel in the organic light emitting display device.

FIG. 2 is a diagram illustrating an embodiment of the DC-DC converter shown in FIG. 1.

Referring to FIG. 2, a switching module 220 of the DC-DC converter 200 according to this embodiment includes an inductor L (or coil), a first switching unit 222 and a second switching unit 224.

The inductor L is coupled between a first node ND 1 and an input terminal for receiving an input voltage VIN. The inductor L increases the voltage level of the input current by generating an electromotive force according to an increase/decrease in input current, caused by the input voltage VIN.

The first switching unit 222 is coupled between the first node ND1 and a ground, and forms or blocks a current path. Specifically, the first switching unit 222 allows the input current to be supplied to or to be blocked from the inductor L, so that the inductor L generates the electromotive force.

The second switching unit 224 is coupled between the first node ND1 and a second node ND2, and forms or blocks the current path. Specifically, the second switching unit 224 allows the input current to be supplied to or to be blocked from the inductor L. The first and second switching units 222 and 224 may generate and output the first voltage V1 while being alternately turned on/off.

A sensing unit 240 is coupled between the second node ND2 and an output node ND_O, and senses driving current I_(D) supplied to a load. The sensing unit 240 may include a shut down switch SW that couples or blocks between the second node ND2 and the output node ND_O, and a sensing voltage output unit 242 that senses driving current I_(D) flowing in the shut down switch SW, and converts the driving current I_(D) into a sensing voltage Vsense and then output the sensing voltage Vsense. To this end, the sensing voltage output unit 242 is coupled to both terminals of the shut down switch SW, so as to detect a voltage drop according to the turn-on resistance of the shut down switch SW. The shut down switch SW is in an off-state when the DC-DC converter 200 is shut down so as to block a leakage current path formed between an input node ND_I and the output node ND_O. The shut down switch SW is turned on/off in response to a control signal CON. The shut down switch SW is turned on in the normal operation of the DC-DC converter 200, and is turned off during the shut-down of the DC-DC converter 200. A resistor is required to sense the driving current I_(D), but in a case where a separate resistor is added, loss additionally occurs due to the separate resistor. Therefore, the turn-on resistance of the shut down switch SW is preferably used.

A control module 260 may control at least one turn-on resistance of the first and second switching units 222 and 224, based on the sensed result of the sensing unit 240. The control module 260 may include a PWM signal generating unit 262 that generates a PWM signal, and a switching control unit 264 that supplies the PWM signal as control signals of the first and second switching units 222 and 224, based on the sensed result of the sensing unit 240.

The PWM signal generating unit 262 generates a PWM signal having a predetermined frequency and provides the generated PWM signal to the switching control unit 264.

The PWM signal generating unit 262 may generate a control signal CON for controlling the shut down switch SW.

The switching control unit 264 generates and outputs the first voltage V1 by increasing the input voltage VIN through a switching operation of alternately turning on/off the first and second switching units 222 and 224. Specifically, in a case where the first switching unit 222 is turned on and the second switching unit 224 is turned off, the first node ND1 is grounded. Accordingly, the current flowing in the inductor L is gradually increased, and a predetermined energy is charged in the inductor L. In a case where the first switching unit 222 is turned off and the second switching unit 224 is turned on, the input voltage VIN and the energy charged in the inductor L are provided to the output node ND_O, and therefore, the first voltage V1 higher than the input voltage VIN is output to the output node ND_O.

The DC-DC converter 200 may be a boost converter that generates the first voltage V1 by boosting the input voltage VIN.

The DC-DC converter 200 may further include a first capacitor C1 coupled between the input node ND_I and the ground, and a second capacitor C2 coupled between the output node ND_O and the ground. In a case where the DC-DC converter 200 according to this embodiment is implemented as a chip, the inductor L of the switching module 220, the first capacitor C1 and the second capacitor C2 may be coupled to the chip from the outside of the chip.

FIG. 3 is a diagram illustrating an embodiment of the switching module 220 shown in FIG. 2.

Referring to FIG. 3, the first switching unit 222 may be configured so that m (m is a natural number of 2 or more) switches MN1 to MNm are coupled in parallel. Each of the m switches MN1 to MNm is coupled in parallel between the first node ND1 and the ground, and may be turned on/off in response to a corresponding control signal NSEL[1:m]. The number of switches turned on according to the control signal NSEL[1:m] is changed, and therefore, the turn-on resistance of the first switching unit 222 may be controlled. For example, a PWM signal may be applied to first and second switches MN1 and MN2 to perform a turn-on/turn-off operations, and a third switch MN3 may maintain an off-state. The switches MN1 to MNm of the first switching unit 222 may be NMOS transistors. Thus, in the first switching unit 222, the size or number of NMOS transistors switched according to the control signal NSEL[1:m] is controlled.

The second switching unit 224 may be configured so that n (n is a natural number of 2 or more) switches MP1 to MPn are coupled in parallel. Each of the n switches MP1 to MPn is coupled in parallel between the first node ND1 and the second node ND2, and may be turned on/off in response to a corresponding control signal PSEL[1:n]. The number of switches turned on according to the control signal PSEL[1:n] is changed, and therefore, the turn-on resistance of the second switching unit 224 may be controlled. For example, a PWM signal may be applied to a first switch MP1 to perform a turn-on/turn-off operation, and second and third switches MP2 and MP3 may maintain the off-state. The switches MP1 to MPn of the second switching unit 224 may be PMOS transistors. Thus, in the second switching unit 224, the size or number of PMOS transistors switched according to the control signal PSEL[1:n] is controlled.

The number of switches of the first switching unit 222 may be identical to that of switches of the second switching unit 224. In this case, the switches of the first switching unit 222 and the switches of the second switching unit 224 may be operated corresponding to each other. For example, in a case where the PWM signal is applied to the first and second switches MN1 and MN2 to perform an turn-on/turn-off operation, and the third switch MN3 of the first switching unit 222 maintains the off-state, the PWM signal may also be applied to the first and second switches MP1 and MP2 of the second switching unit 224 to perform a turn-on/turn-off operation, and the third switch MP3 of the second switching unit 224 may maintain the off-state.

FIG. 4 is a diagram illustrating an embodiment in which the first and second switching units 222 and 224 of the DC-DC converter 200 shown in FIG. 2 each has three transistor switches.

Referring to FIG. 4, a DC-DC converter 400 according to an embodiment of the present invention includes a switching module 420, a sensing unit 440 and a control module 460.

The switching module 420 includes an inductor L, a first switching unit 422 and a second switching unit 424. In the first switching unit 422, three NMOS transistors MN1 to NM3 are coupled in parallel between a first node ND1 and a ground. In the second switching unit 424, three PMOS transistors MP1 to MP3 are coupled in parallel between the first node ND1 and a second node ND2.

The sensing unit 440 is coupled between the second node ND2 and an output node ND_O, and senses a load condition. Specifically, the sensing unit 440 includes a shut down switch SW coupled between the second node ND2 and the output node ND_O, and a sensing voltage output unit 442 that senses a voltage applied to both terminals of the shut down switch SW. A PMOS transistor may be used as the shut down switch.

The control module 460 includes a PWM signal generating unit 462 and a switching control unit 464.

The PWM signal generating unit 462 generates a PWM signal having a predetermined period and a predetermined pulse width.

The switching control unit 464 controls the NMOS transistors MN1 to MN2 of the first switching unit 422 and the PMOS transistors MP1 to MP3 of the second switching unit 424 according to the sensed result of the sensing unit 440. For example, under a light load condition in which the sensing voltage Vsense sensed in the sensing unit 440 is smaller than a first reference voltage Vref1, only one switch MN1 of the first switching unit 422 and one switch MP1 of the second switching unit 424 may be PWM-controlled, and the other switches MN2 and MN3 of the first switching unit 422 and switches MP2 and MP3 of the second switching unit 424 may maintain an off-state. Under a medium load condition in which the sensing voltage Vsense sensed in the sensing unit 440 is greater than the first reference voltage Vref1 and smaller than a second reference voltage Vref2, the two switches MN1 and MN2 of the first switching unit 422 and the two switches MP1 and MP2 of the second switching unit 424 may be PWM-controlled, and the other switch MN3 of the first switching unit 422 and the switch MP3 of the second switching unit 424 may maintain the off-state. Under a heavy load condition in which the sensing voltage Vsense sensed in the sensing unit 440 is greater than the second reference voltage Vref2 and smaller than a third reference voltage Vref3, the three switches MN1, NM2 and MN3 of the first switching unit 422 and MP1, MP2 and MP3 of the second switching unit 424 may be PWM-controlled. In a case where the sensing voltage Vsense sensed in the sensing unit 440 is greater than the third reference voltage Vref3, a short circuit, etc. occurred at a load. In this case, all the switches of the first and second switching units 422 and 424 may be turned off. Thus, the switching control unit 460 controls the first and second switching units 422 and 424 so that the turn-on resistance of the first and second switching units 422 and 424 is greatest under the light load condition, and controls the first and second switching units 422 and 424 so that the turn-on resistance of the first and second switching units 422 and 424 is smallest under the heavy load condition, thereby minimizing loss of the DC-DC converter 400.

The switching control unit 464 may include a comparison unit 467 having first to third comparators that respectively compare sensing voltages Vsense output from the sensing unit 440 with the first to third reference voltages Vref1 to Vref3, and a control signal supply unit 466 that supplies a PWM signal to the switches of the first and second switching units 422 and 424, based on an output of the comparison unit 467.

Each of the first to third comparators of the comparison unit 467 may output a low signal when the sensing voltage Vsense is smaller than the corresponding reference voltage, and may output a high signal when the sensing voltage Vsense is greater than or identical to the corresponding reference voltage. For example, in case where the sensing voltage Vsense is smaller than the first reference voltage Vref1 that is smaller than the second reference voltage Vref2 that is smaller than the third reference voltage Vref3 (Vsense<Vref1<Vref2<Vref3), the first to third comparators may all output the low signal. In case where the first reference voltage Vref1 is smaller than or equal to the sensing voltage Vsense that is smaller than the second reference voltage Vref2 that is smaller than the third reference voltage Vref3 (Vref1<Vsense<Vref2<Vref3), the first comparator may output the high signal, and the second and third comparators may output the low signal. In a case where the first reference voltage Vref1 is smaller than the second reference voltage Vref2 that is smaller than or equal to the sensing voltage Vsense that is smaller than the third reference voltage Vref3 (Vref1<Vref2<Vsense<Vref3), the first and second comparators may output the high signal, and the third comparator may output the low signal. In a case where the first reference signal Vref1 is smaller than the second reference signal Vref2 that is smaller than the third reference signal Vref3 that is smaller than or equal to the sensing voltage Vsense (Vref1<Vref2<Vref3<Vsense), the first to third comparators may all output the high signal.

The switching control unit 464 may further include a soft start 468. That is, in a case where the third comparator outputs the high signal in the switching control unit 460, there may exist a failure due to a short circuit, etc., which occurs at the load. In a case where a certain current or more flows in the load, it is possible to cut off the current by shutting down the DC-DC converter.

FIG. 5 is a diagram illustrating another embodiment of the DC-DC converter 100 shown in FIG. 1.

Referring to FIG. 5, in a DC-DC converter 500 according to this embodiment, a switching module 520 includes a first switching unit 522, an inductor L (or coil) and a second switching unit 524. The first switching unit 522 is coupled between a first node ND1 and an input node ND_I for receiving an input voltage VIN, and forms or blocks a current path. The inductor L is coupled between the first node ND1 and a ground, and generates an electromotive force, based on an increase/decrease in input current according to the input voltage VIN. The second switching unit 524 is coupled between the first node ND1 and a second node ND2, and forms or blocks a current path.

The first switching unit 522 is coupled between the input node ND_I and the first node ND1, and forms or blocks the current path. Specifically, the first switching unit 522 allows input current to be supplied to or blocked from the inductor L, so that an electromotive force is generated in the inductor L.

The second switching unit 524 is coupled between the first node ND1 and the second node ND2, and forms or blocks the current path. Specifically, the second switching unit 524 supplies or blocks a back electromotive force formed in the inductor L while the input current is blocked.

The first and second switching units 522 and 524 may generate and output a first voltage V1 while being alternately turned on/off.

A sensing unit 540 is coupled between the second node ND2 and an output node ND_O, and senses driving current I_(D). The sensing unit 540 may include a shut down switch SW that couples or blocks between the second node ND2 and the output node ND_O, and a sensing voltage output unit 542 that converts the driving current I_(D) flowing in the shut down switch SW into a sensing voltage Vsense and outputs the sensing voltage Vsense. To this end, the sensing voltage output unit 542 is coupled to both terminals of the shut down switch SW, so as to detect a voltage drop according to the turn-on resistance of the shut down switch SW. The shut down switch SW is in an off-state when the DC-DC converter 500 is shut down so as to block a leakage current path formed between the input node ND_I and the output node ND_O. The shut down switch SW is turned on/off in response to a control signal CON. The shut down switch SW is turned on in the normal operation of the DC-DC converter 500, and is turned off in the shut down of the DC-DC converter 500. A resistor is required to sense the driving current ID, but in a case where a separate resistor is added, loss additionally occurs due to the separate resistor. Therefore, the turn-on resistance of the shut down switch SW is preferably used.

A control module 560 may control at least one turn-on resistance of the first and second switching units 522 and 524, based on the sensed result of the sensing unit 540.

The control module 560 may include a PWM signal generating unit 562 that generates a PWM signal, and a switching control unit 564 that supplies the PWM signal as control signals of the first and second sensing units 522 and 524, based on the sensed result of the sensing unit 540.

The PWM signal generating unit 562 generates a PWM signal having a predetermined frequency and provides the PWM signal to the switching control unit 564. The PWM signal generating unit 562 may generate a control signal for controlling the shut down switch SW.

The switching control unit 564 generates and outputs the first voltage V1 by increasing the input voltage VIN through a switching operation of alternately turning on/off the first and second switching units 522 and 524. Specifically, in a case where the first switching unit 522 is turned on and the second switching unit 524 is turned off, the input voltage VIN is applied to the first node ND1. Accordingly, the current flowing in the inductor L is gradually increased, and a predetermined energy is charged in the inductor L. In a case where the first switching unit 522 is turned off and the second switching unit 524 is turned on, the energy charged in the inductor L is represented in the form of a back electromotive force at both terminals of the inductor L as the flow of current is suddenly cut off and then provided to the output node ND_O. Therefore, the first voltage V1 having a polarity different from that of the input voltage VIN is output to the output node ND_O.

The DC-DC converter 500 may be an inverting buck-boost converter that generates the first voltage by inverting the input voltage VIN.

The DC-DC converter 500 may further include a first capacitor C1 coupled between the input node ND_I and the ground, and a second capacitor C2 coupled between the output node ND_O and the ground. In a case where the DC-DC converter 500 according to this embodiment is implemented as a chip, the inductor L of the switching module 520, the first capacitor C1 and the second capacitor C2 may be coupled to the chip from the outside of the chip.

FIG. 6 is a diagram illustrating an embodiment of the switching module 520 shown in FIG. 5.

Referring to FIG. 6, the first switching unit 522 may be configured so that n (n is a natural number of 2 or more) switches MP1 to MPn are coupled in parallel. Each of the n switches MP1 to MPn is coupled in parallel between the input node ND_I and the first node ND1, and may be turned on/off in response to a corresponding control signal. The number of switches turned on according to a control signal PSEL[1:n] is changed, and therefore, the turn-on resistance of the first switching unit 522 may be controlled. For example, a PWM signal may be applied to first and second switches MP1 and MP2 to perform a turn-on/turn-off operation, and a third switch MP3 may maintain an off-state. The switches of the first switching unit 522 may be PMOS transistors. Thus, in the first switching unit 522, the size or number of PMOS transistors switched according to the control signal is controlled.

The second switching unit 524 may be configured so that m (m is a natural number of 2 or more) switches MN1 to MNm are coupled in parallel. Each of the m switches MN1 to MNm is coupled in parallel between the first node ND1 and the second node ND2, and may be turned on/off in response to a corresponding control signal. The number of switches turned on according to a control signal NSEL[1:m] is changed, and therefore, the turn-on resistance of the second switching unit 524 may be controlled. For example, a PWM signal may be applied to a first switch MN1 to perform a turn-on/turn-off operation, and second and third switches MN2 and MN3 may maintain an off-state. The switches of the second switching unit 524 may be NMOS transistors. Thus, in the second switching unit 524, the size or number of NMOS transistors switched according to the control signal is controlled.

The number n of the switches of the first switching unit 522 may be identical to that m of the switches of the second switching unit 524. In this case, the switches MP1 to MPn of the first switching unit 522 and the switches MN1 to MNm of the second switching unit 524 may be operated corresponding to each other. For example, in a case where the PWM signal is applied to the first and second switches MP1 and MP2 of the first switching unit 522 to perform the turn-on/turn-off operation, and the third switch MP3 of the first switching unit 522 maintains the off-state, the PWM signal may also be applied to the first and second switches MN1 and MN2 of the second switching unit 524 to perform the turn-on/turn-off operation, and the third switch MN3 of the second switching unit 524 may maintain the off-state.

FIG. 7 is a diagram illustrating an embodiment in which the first and second switching units 522 and 524 of the DC-DC converter 500 shown in FIG. 5 each has three transistor switches.

Referring to FIG. 7, a DC-DC converter 700 according to an embodiment of the present invention includes a switching module 720, a sensing unit 740 and a control module 760.

The switching module 720 includes a first switching unit 722, an inductor L and a second switching unit 724.

In the first switching unit 722, three PMOS transistors MP1, MP2 and MP3 are coupled in parallel between an input node ND_1 and a first node ND1.

The inductor L is coupled between the first node ND1 and a ground.

In the second switching unit 724, three NMOS transistors MN1, MN2 and MN3 are coupled in parallel between the first node ND1 and a second node ND2.

The sensing unit 740 is coupled between the second node ND2 and an output node ND_O, and senses a load condition. Specifically, the sensing unit 740 includes a shut down switch SW coupled between the second node ND2 and the output node ND_O, and a sensing voltage output unit 442 that senses a voltage applied to both terminals of the shut down switch SW and outputs a sensing voltage Vsense. An NMOS transistor may be used as the shut down switch SW.

The control module 760 is similar to the control module 460 of the embodiment of FIG. 4, and therefore, its detailed description will be omitted.

FIG. 8 is a diagram illustrating an organic light emitting display device according to an embodiment of the present invention.

Referring to FIG. 8, the organic light emitting display device 800 according to this embodiment includes a display panel 820, a timing controller 840 and a DC-DC converter 860.

The display panel 820 has a plurality of pixels, and displays a gray scale according to the luminance of an organic light emitting diode in each pixel.

The timing controller 840 provides data to the display panel 820 to display an image, and may provide a scan signal and a data signal to the display panel 820.

The DC-DC converter 860 generates first and second voltages V1 and V2 for supplying current to the organic light emitting diode by receiving an input voltage VIN, and provides the generated first and second voltages V1 and V2 to the display panel 820. The first voltage V1 is a voltage ELVDD applied to an anode of the organic light emitting diode in each pixel of the display panel 820, and the second voltage V2 is a voltage ELVSS applied to a cathode of the organic light emitting diode in each pixel of the display panel 820.

The DC-DC converter 860 includes a first converter 870 that converts the input voltage VIN into the first voltage V1 and outputs the first voltage V1, a second converter 880 that converts the input voltage VIN into the second voltage V2 and outputs the second voltage V2, and a sensing unit 890 that senses driving current I_(D) supplied to the display panel 820.

The first converter 870 generates the first voltage V1 by increasing the input voltage VIN, and the second converter 880 generates the second voltage V2 by reversing the polarity of the input voltage VIN and decreasing the input voltage VIN.

In the first and second converters 870 and 880, switching loss according the parasitic capacitance of switching transistors of first and second switching modules 872 and 882 increases when the display panel 820 displays an image with low luminance, and the driving current ID increases when the display panel 820 displays an image with high luminance. Therefore, conduction loss according to the turn-on resistance of the switching transistors increases. Thus, first and second control modules 874 and 884 operate to minimize the switching loss when the display panel 820 displays the image with the low luminance, and operate to minimize the conduction loss when the display panel 820 displays the image with the high luminance.

As a result, the organic light emitting display device 800 according to this embodiment can have optimal efficiency, regardless of various load conditions.

The first converter 870 includes the first switching module 872 and the first control module 874.

The first switching module 872 has a plurality of switches. Each of the switches converts an input voltage VIN applied from the outside of the first switching module 872 into a first voltage V1 and outputs the first voltage V1 while being switched in response to a corresponding PWM signal.

The first control module 874 controls the first switching module 872 by generating a PWM signal. The first control module 874 is configured to adaptively control the turn-on resistance of the first switching module 872 according to the sensed result of the sensing unit 890. In other words, the first control module 874 is configured to adaptively control the size of a switch or transistor in the first switching module 872 according to a load condition.

The second converter 880 includes the second switching module 882 and the second control module 884.

The first switching module 882 has a plurality of switches. Each of the switches converts the input voltage VIN applied from the outside of the second switching module 882 into a second voltage V1 and outputs the second voltage V1 while being switched in response to a corresponding PWM signal.

The second control module 884 controls the second switching module 882 by generating a PWM signal. The second control module 884 is configured to adaptively control the turn-on resistance of the second switching module 882 according to the sensed result of the sensing unit 890. In other words, the second control module 884 is configured to adaptively control the size of a switch or transistor in the second switching module 882 according to a load condition.

The sensing unit 890 senses driving current I_(D) supplied to the display panel 820 at an output terminal of the first converter 870, i.e., a first output node ND_O1 at which the first voltage V1 is output. For example, in a case where the capacity of the load is changed while the first and second voltages V1 and V2 are supplied to the load, i.e., in a case where the driving current I_(D) supplied to each pixel of the display panel 820 is changed, the sensing unit 890 senses, in real time, a change in driving current and informs the first and second control modules 874 and 884 of the sensed change in driving current.

FIG. 9 is a diagram illustrating an embodiment of the DC-DC converter 860 shown in FIG. 8.

Referring to a DC-DC converter 960 includes a first converter 970, a second converter 980 and a sensing unit 990.

The first converter 970 include a first switching module 972, a first control module 974. The second converter 980 includes a second switching module 982 and a second control module 984.

The first switching module 972 includes a first inductor L1, a first switching unit 972_2 and a second switching unit 972_4. The first control module 974 includes a first PWM signal generating unit 974_2 and a first switching control unit 974_4.

The second switching module 982 includes a third switching unit 982_2, a second inductor L2 and a fourth switching unit 982_4. The second control module 984 includes a second PWM signal generating unit 984_2 and a second switching control unit 984_4.

The sensing unit 990 includes a shut down switch SW and a sensing voltage output unit 992 coupled in parallel with the shut down switch SW. The sensing unit 990 senses the amount of current supplied to the display panel from the output node ND_O1, and outputs a sensing voltage Vsense to the first and second control modules 974 and 984.

An embodiment of the first switching module 972 is the same as that shown in FIG. 3.

In a case where the first switching module 972 has the configuration of the switching module 420 shown in FIG. 4, an embodiment of the first control module 974 has the same configuration of the control module 460 shown in FIG. 4.

An embodiment of the second switching module 982 is the same as that shown in FIG. 6.

In a case where the second switching module 982 has the configuration of the switching module 720 shown in FIG. 7, an embodiment of the second control module 984 has the same configuration as the control module 760 shown in FIG. 7.

Although it has been illustrated in FIG. 9 that the first and second switching units 972_2 and 972_4 are controlled by the first switching control unit 974_4 and the third and fourth switching units 982_2 and 982_4 are controlled by the second switching control unit 984_4, the first to fourth switching units 972_2, 972_4, 982_2 and 982_4 may be controlled by one switching control unit.

The DC-DC converter 960 of the organic light emitting display device 800 according to this embodiment may further include a first capacitor C1 coupled between an input node ND_1 and a ground, a second capacitor C2 coupled between a first output node ND_O1 and the ground, and a third capacitor C3 coupled between a second output node ND_O2 and the ground.

In a case where the DC-DC converter 960 is implemented as a semiconductor chip, the first inductor L1 of the first switching module 972, the second inductor L2 of the second switching module 982, the first capacitor C1, the second capacitor C2 and the third capacitor C3 may be coupled to the semiconductor chip from the outside of the semiconductor chip.

FIG. 10 is a diagram illustrating an organic light emitting display device 1000 according to another embodiment of the present invention.

Referring to FIG. 10, the organic light emitting display device 1000 according to this embodiment is different from that of the embodiment of FIG. 8 in the position of a sensing unit 1090 of a DC-DC converter 1060. In the embodiment of FIG. 8, the sensing unit 890 of the DC-DC converter 860 is positioned at the output terminal of the first converter 870 so as to sense driving current ID. On the other hand, in the embodiment of FIG. 10, the sensing unit 1090 of the DC-DC converter 1060 is positioned at an output terminal of a second converter 1080 so as to sense driving current ID.

FIG. 11 is a diagram illustrating an embodiment of the DC-DC converter 1060 shown in FIG. 10.

Referring to FIG. 11, the DC-DC converter 1160 according to this embodiment is different from that of the embodiment of FIG. 9 in the position of the sensing unit 1090. That is, in the embodiment of the FIG. 9, the sensing unit 990 is positioned at the output terminal of the first converter 970 so as to sense driving current. On the other hand, in the embodiment of FIG. 11, the sensing unit 1190 is positioned at an output terminal of the second converter 1180 so as to sense driving current.

While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof. 

What is claimed is:
 1. A DC-DC converter, comprising: a switching module that converts an input voltage into a first voltage through switching operations of a plurality of switches that are turned on or off in response to a pulse width modulation (PWM) signal, and outputs the first voltage; a sensing unit that senses driving current supplied to a load to which the first voltage is provided; and a control module that controls the switching module by generating the PWM signal, the control module being configured to adaptively control the turn-on resistance of the switching module according to the sensed result of the sensing unit.
 2. The DC-DC converter according to claim 1, wherein the switching module comprises: an inductor coupled between a first node and an input node to which the input voltage is applied; a first switching unit coupled between the first node and a ground so as to form or block a current path; and a second switching unit coupled between the first node and a second node so as to form or block a current path, wherein the sensing unit is coupled between the second node and an output node so as to sense the driving current, and the control module controls the turn-on resistance of at least one of the first and second switching units, based on the sensed result of the sensing unit.
 3. The DC-DC converter according to claim 2, wherein, when the driving current increases, the control module decreases the turn-on resistance of at least one of the first and second switching units.
 4. The DC-DC converter according to claim 2, wherein at least one of the first and second switching units includes a plurality of switches coupled in parallel.
 5. The DC-DC converter according to claim 4, wherein the control module controls a number of switches turned on among the plurality of switches, based on the sensed result of the sensing unit.
 6. The DC-DC converter according to claim 4, wherein the first switching unit includes a plurality of NMOS transistors coupled in parallel, and the second switching unit includes a plurality of PMOS transistors coupled in parallel.
 7. The DC-DC converter according to claim 4, wherein the control module comprises: a PWM signal generating unit that generates the PWM signal; and a switching control unit that supplies the PWM signal as control signals of the first and second switching units, based on the sensed result of the sensing unit.
 8. The DC-DC converter according to claim 7, wherein the sensing unit comprises: a shut down switch that forms or blocks a current path between the second node and the output node; and a sensing voltage output unit that converts the driving current flowing in the shut down switch into a sensing voltage, and outputs the sensing voltage.
 9. The DC-DC converter according to claim 8, wherein the switching control unit comprises: at least one comparison unit that compares the sensing voltage with a reference voltage; and a control signal supply unit that supplies the PWM signal to corresponding switches among the plurality of switches, based on the output of the at least one comparison unit.
 10. The DC-DC converter according to claim 9, wherein the at least one comparison unit outputs a high signal when the sensing voltage is greater than or identical to the corresponding reference voltage.
 11. The DC-DC converter according to claim 1, wherein the switching module comprises: a first switching unit coupled between a first node and an input node to which the input voltage is input so as to form or block a current path; an inductor coupled between the first node and a ground; and a second switching unit coupled between the first node and a second node so as to form or block a current path, wherein the sensing unit is coupled between the second node and an output node so as to sense the driving current, and the control module controls the turn-on resistance of at least one of the first and second switching units, based on the sensed result of the sensing unit.
 12. The DC-DC converter according to claim 11, wherein, when the driving current increases, the control module decreases the turn-on resistance of at least one of the first and second switching units.
 13. The DC-DC converter according to claim 11, wherein at least one of the first and second switching units includes a plurality of switches coupled in parallel.
 14. The DC-DC converter according to claim 13, wherein the control module controls a number of switches turned on among the plurality of switches, based on the sensed result of the sensing unit.
 15. The DC-DC converter according to claim 13, wherein the first switching unit includes a plurality of PMOS transistors coupled in parallel, and the second switching unit includes a plurality of NMOS transistors coupled in parallel.
 16. The DC-DC converter according to claim 13, wherein the control module comprises: a PWM signal generating unit that generates the PWM signal; and a switching control unit supplies the PWM signal as control signals of the first and second switching units, based on the sensed result of the sensing unit.
 17. The DC-DC converter according to claim 16, wherein the sensing unit comprises: a shut down switch that couples or blocks between the second node and the output node; and a sensing voltage output unit that converts the driving current flowing in the shut down switch into a sensing voltage, and outputs the sensing voltage.
 18. The DC-DC converter according to claim 17, wherein the switching control unit comprises: at least one comparison unit that compares the sensing voltage with a reference voltage; and a control signal supply unit supplies the PWM signal to corresponding switches among the plurality of switches, based on the output of the at least one comparison unit.
 19. The DC-DC converter according to claim 18, wherein at least one comparison unit outputs a high signal when the sensing voltage is greater than or identical to the corresponding reference voltage.
 20. An organic light emitting display device, comprising: a display panel that has a plurality of pixels, and displays a gray scale according to the luminance of an organic light emitting diode in each pixel; a timing controller that provides data to the display panel; and a DC-DC converter that generates first and second voltages for supplying current to the organic light emitting diode by receiving an input voltage, and provides the first and second voltages to the display panel, wherein the DC-DC converter comprises: a first converter that converts the input voltage into the first voltage, and outputs the first voltage; a second converter that converts the input voltage into the second voltage, and outputs the second voltage; and a sensing unit that senses driving current supplied to the display panel, wherein the first converter comprises: a first switching module that converts the input voltage into the first voltage through switching operations of a plurality of switches that are turned on or off in response to a first PWM signal, and outputs the first voltage to the display panel; and a first control module that controls the switching module by generating the first PWM signal, wherein the second converter comprises: a second switching module that converts the input voltage into the second voltage through switching operations of a plurality of switches that are turned on or off in response to a second PWM signal, and outputs the second voltage to the display panel; and a second control module that controls the second switching module by generating the second PWM signal, wherein the first control module is configured to adaptively control the turn-on resistance of the first switching module, based on the sensed result of the sensing unit, and the second control module is configured to adaptively control the turn-on resistance of the second switching module, based on the sensed result of the sensing unit.
 21. The organic light emitting display device according to claim 20, wherein the first switching module comprises: a first inductor coupled between a first node and an input node to which the input voltage is input; a first switching unit coupled between the first node and a ground so as to form or block a current path; and a second switching unit coupled between the first node and a second node so as to form or block a current path, wherein the sensing unit is coupled between the second node and a first output node from which the first voltage is output so as to sense the driving current, the first control module controlling the turn-on resistance of at least one of the first and second switching units, based on the sensed result of the sensing unit, wherein the second switching module comprises: a third switching unit coupled between the input node and a third node so as to form or block a current path; a second inductor coupled between the third node and the ground; and a fourth switching unit coupled between the third node and a second output node from which a third voltage is output so as to form or block a current path, wherein the second control module controls the turn-on resistance of at least one of the third and fourth switching units, based on the sensed result of the sensing unit.
 22. The organic light emitting display device according to claim 21, wherein when the driving current increases, the first control module decreases the turn-on resistance of at least one of the first and second switching units, and when the driving current increases, the second control module decreases the turn-on resistance of at least one of the third and fourth switching units.
 23. The organic light emitting display device according to claim 21, wherein at least one of the first and second switching units includes a plurality of switches coupled in parallel, and at least one of the third and fourth switching units includes a plurality of switches coupled in parallel.
 24. The organic light emitting display device according to claim 23, wherein the first and second control modules control a number of switches that are turned on among the plurality of switches of the corresponding switching unit, based on the sensed result of the sensing unit.
 25. The organic light emitting display device according to claim 21, further comprising: a first capacitor coupled between the input node and the ground; a second capacitor coupled between the first output node and the ground; and a third capacitor coupled between the second output node and the ground.
 26. The organic light emitting display device according to claim 20, wherein the first switching module comprises: a first inductor coupled between a first node and an input node to which the input voltage is input; a first switching unit coupled between the first node and a ground so as to form or block a current path; and a second switching unit coupled between the first node and a first output node from which the first voltage is output, wherein the first control module controls the turn-on resistance of at least one of the first and second switching units, based on the sensed result of the sensing unit, the second switching module comprising: a third switching unit coupled between the input node and a second node so as to form or block a current path; a second inductor coupled between the second node and the ground; and a fourth switching unit coupled between the second node and a third node so as to form or block a current path, wherein the sensing unit coupled between the third node and a second output node from which the second voltage is output so as to sense the driving current, wherein the second control module controls the turn-on resistance of at least one of the third and fourth switching units, based on the sensed result of the sensing unit.
 27. The organic light emitting display device according to claim 26, wherein, when the driving current increases, the first control module decreases the turn-on resistance of at least one of the first and second switching units, and when the driving current increases, the second control module decreases the turn-on resistance of at least one of the third and fourth switching units.
 28. The organic light emitting display device according to claim 26, wherein at least one of the first and second switching units includes a plurality of switches coupled in parallel, and at least one of the third and fourth switching units includes a plurality of switches coupled in parallel.
 29. The organic light emitting display device according to claim 28, wherein the first and second control modules control a number of switches that are turned on among the plurality of switches of the corresponding switching unit, based on the sensed result of the sensing unit.
 30. The organic light emitting display device according to claim 26, further comprising: a first capacitor coupled between the input node and the ground; a second capacitor coupled between the first output node and the ground; and a third capacitor coupled between the second output node and the ground. 